The interrelationships between calcium, cyclic AMP, and metabolites of arachidonic acid in the regulation of platelet function will be studied. Localization of enzymes involved in Ca2 ion-transport, and cAMP prostaglandin and thromboxane synthesis will be studied in fractions of platelet homogenates, and in intact cells by cytochemistry. The effects of platelet stimuli and inhibitors on cellular Ca2 ion transport will be studied. The involvement of a stimulus-activated serine protease (esterase) in prostaglandin metabolism will be investigated. Studies on a heat-stable platelet protein which stimulates phosphorylation of platelet myosin by a specific LC-protein kinase will also be continued. The objective of this study is to elucidate the sites of storage of platelet calcium, the mechanisms by which it is mobilized by various stimuli, and the mechanisms by which Ca2 ion then activates platelet aggregation, the release reaction, and prostaglandin and thromboxane formation. Furthermore, we shall investigate how cAMP, prostaglandins and thromboxanes are involved in regulation of a. the Ca2 ion metabolism of the platelet and b. the Ca2 ion-dependent reactions which are initiated by platelet stimulation.